The reason for seven, yes some people Will disagree and say wait for the other appliances
A few examples
House fire
4 in BA, 1 IOC, 1 Pump operator, 1 person getting water in = 7
Grass Fire 1 Line
1 IOC, 1 Pump operator, 5 on one Line ( 90m is a lot of hose to get working with in some areas)
If you went to a job like Mt Osmond 1 line with a crew of seven was still hard work on a day like that, the more the better, it must be safer less work than six
Grass Fire 2 Lines
1 IOC, 1 Pump operator, 3 on one line and 2 on the other.
House Fire:
2xBA(takes 38mm hose/branch to entry) 1xPump Operator(stretches 64mm to 38mm for entry, sinks Hydrant) 1xOIC/ECO.
Works with 4. If you have a spare person or two, they should be streching the lne to the front door, and/or sinking the hydrant. THEN those people spare can don BA. You won't have 4xBA going in without another appliance being there.
I went to Mt. Osmond, spent the day up and down goat country with 90m hose reels, plus canvas on the end, crew of 4. No issues what so ever. Maybe you need to teach your No. 2 on the hose how to haul hose correctly?